Prior art systems such as U.S. Pat. No. 3,556,439, Method and High Lift Systems for Making an Aircraft Wing more Efficient for Takeoff and Landings, by Charles P. Autrey et al, provide a large increase in wing area and camber by extending and drooping the front portion of the airfoil and further extending a three segment leading edge flap downwardly and forwardly of the leading edge. While having the advantages noted above, such designs have the disadvantage of being extremly complicated and they occupy a considerable amount of space in the wing which could otherwise be used to store fuel.
In order to reduce the volume occupied by a multisegment leading edge flap, past designs have attempted to make use of a portion of the bottom surface of the airfoil as a flap segment. For example, U.S. Pat. No. 3,504,870, Aircraft Wing Variable Camber Leading Edge Flap, by J. B. Cole et al., uses a relatively flat portion of the bottom surface of the airfoil which extends forwardly and downwardly from the leading edge. The flat portion is then warped into an aerodynamic surface by a sophisticated linkage system. While this design reduces the volume occupied by the leading edge flap, it still requires a complex actuation mechanism.
Another approach can be found in U.S. Pat. No. 3,831,886, Airfoil with Extendable and Retractable Leading Edge, by Kenneth P. Burgess et al. In this design, the leading edge is pivoted outwardly and downwardly to form an aerodynamic extension of the airfoil. Its main drawback is that it requires the pivot point to be external of the airfoil's contour. Thus the support linkages must extend downward from the bottom surface of the airfoil, increasing drag. Another drawback of this invention is that only a relatively small increase in wing area is achieved.
Another approach, and quite an old one, is to simply rotate the leading edge of the airfoil, as disclosed in U.S. Pat. No. 1,631,259, Variable Lift, Variable Resistance Airfoil, by W. L. Gilmour. A roughly triangular shaped leading edge is adapted to be rotated to slightly change the camber of the airfoil. While occupying a minimum space, it has little effect on wing area and, as previously mentioned, provides only a small increase in camber.
Another problem of which the prior art leading edge flap designs have not addressed is the provision of means for deicing. The conventional method for deicing a wing is to distribute heated air; for example, by bleeding air from the engines and directing it spanwise along the forward portion of the airfoil to melt any ice forming on the top surface of the airfoil. It is quite difficult to run ducts of sufficient size in an optimum position when using the prior art leading edge flap designs because, as previously mentioned, they have sophisticated linkage systems and/or occupy a considerable amount of the airfoil's volume.
It is also a desirable feature to have some form of boundary layer control typically provided by ejecting air over the top surface of the airfoil. This assures that at any given speed the boundary layer does not separate until a much higher angle of attack and higher coefficient of lift are reached.
The previously mentioned Burgess et al design does provide for boundary layer control. But the very fact that the leading edge is translated forward requires a flexible connection between the leading edge and the air supply ducts. This has disadvantages in that such flexible connections are subject to fatigue failure.
From the foregoing, it can be seen that it is a primary object of this invention to provide a leading edge flap that can be stored within the airfoil in a minimal space when retracted. This is accomplished while still providing, when the flap is extended, a significant increase in wing area and camber, as well as a larger effective leading edge radius than is provided by leading edge flaps which are pivoted at or near the leading edge.
It is also an object of this invention to provide a leading edge flap having a simplified actuation system, with all hinge brackets and actuators being located inside the airfoil contour.
A further object of this invention is to provide a leading edge flap having provisions for deicing the airfoil.
A still further object of this invention is to provide a leading edge flap having provisions for boundary layer control.